The present invention is related to a method for treating high-concentrated organic wastewater, such as night soil or livestock wastewater, which has high levels of nitrogen and phosphorous. In particular, it is related to a method for treating night soil or livestock wastewater having high levels of nitrogen and phosphorous, comprising an anaerobic ammonium oxidizing (Anammox) step and a biopond step.
The treatment of night soil or livestock wastewater has been regarded as a difficult and troublesome problem. No technique has been recognized as being the perfect solution even though many approaches have been taken. Usually, night soil or livestock wastewater is first collected into one place and treated by a locally shared treatment plant because sharing a treatment plant provides the advantage of convenient management and operation. However, such shared treatment plants have never demonstrated any success in removing high levels of organic material and nitrogen, which is generally found in extremely higher concentrations than those expected from an amount of organic material in night soil or livestock wastewater.
Furthermore, another conventional method of treating very highly concentrated night soil or livestock wastewater is dilution. However, the dilution is not efficient in that it requires consumption of an extremely large amount of water. For example, treating livestock wastewater having 15,000 mg/L of BOD by dilution needs 75 times this amount of water. Moreover, the dilution procedure requires a sufficiently large plant to hold this large amount of water. This leads to increase costs in building plants, in aerating the plant, and in fitting complementary equipment.
Other conventional methods for treating night soil or livestock wastewater focus on the removal of organic material and, thus, can not provide an efficient means for removing nitrogen or phosphorous, even though nitrogen and phosphorous are recognized as the main contaminants that causes eutrophication of lakes and marshes.
Studies have been made on various methods for treating night soil or livestock wastewater. In the removal of nitrogen from livestock wastewater, rates of variation in loading have been investigated in Bortone G., Gemeli, S. and Rambaldi, A. xe2x80x9cNitrification, Denitrification and Biological Phosphate Removal in SBR Treating Piggery Wastewaterxe2x80x9d, Wat, Sci. Tech., Vol, No. 5-6, p 977-985, 1992), which describes a ratio of an average flow rate per day to a maximum flow rate per day as 1.43, and a ratio of a maximum to a minimum of flow rate per hour as being more than 8.
According to Strous, M. et al., it takes about 1 year to make compliant Anammox-causing microorganisms, and such microorganisms have good sedimentation properties and an activity of 0.02 mg NH4+-N/mg biomass/hr (Strous, M., heijnen, J., Kuenen, J., G. and Jetten, M. S. M. xe2x80x9cThe sequencing batch reactor as a powerful tool for the study of slowly growing anaerobic ammonium-oxidizing microorganismsxe2x80x9d, Appl. Microbiol. Biotechnol., Vol. 50, p 589-596, 1998). According to Van de Graff, A. A. et al., Anammox activity is 66 ng NH4+-N/mg VS/hr, and this activity can be affected even by an extremely small amount of O2 and depends absolutely on NO3xe2x88x92. The amount of microorganisms is directly proportionate to the biomass in the culture bath (Van de Graff, A. A., Mulder, A., de Bruijn, P., Jetten, M. S. M., Robertson, L. A. and Kuenen, J. G., xe2x80x9cAnaerobic oxidation of ammonium in a biologically mediated processxe2x80x9d, Appl. Environ. Microbiol. Vol. 61, p. 1246-1251, 1995).
A study has been reported to quantify ammonia volatilization from a piggery pond in order to determine its significance as a nitrogen removal mechanism (Andy, S., xe2x80x9cAmmonia volatilization from a piggery pondxe2x80x9d, Wat. Sci. Tech., Vol. 33, No. 7, p 183-199, 1996). The rate of ammonia volatilization greatly varies within the range of 355 to 1534 mg/m2/d, depending on the pH. Upon the volatilization of ammonia, the pH and the COD tend to decrease slowly.
The removal efficiency rate of total nitrogen (TK) from piggery wastewater was 86% when a reactor was operated with mixed liquor suspended solids (MLSS) being 17,000 mg/L during an intermittent aeration process. (Josxc3xa9 R. Bicudo and Ivo F. Svoboda, xe2x80x9cIntermittent aeration of pig slurryxe2x80x94farm scale experiments for carbon and nitrogen removal,xe2x80x9d Wat. Sci. Tech., Vol 32 No 12 pp 83-90, 1995)
The objective of this invention is to provide a method for the treatment of wastewater having high concentrations of nitrogen and phosphorus, such as night soil or livestock, and an apparatus used therefor.
In order to achieve the above objective, we, the applicants, provide a novel method for the treatment of wastewater that includes an Anammox step and a biopond step. This method adopts solid-liquid separation instead of dilution with water.
In particular, this method comprises the following steps:
(a) equalizing a flow rate and an amount of concentrated wastewater having at least 10,000 mg/L of BOD in an equalization tank,
(b) carrying out solid-liquid separation of the equalized wastewater from step (a) by adding an aggregating agent thereto so that the concentrations of organic material and nitrogen can be adjusted to desired levels,
(c) stripping ammonia selectively from the wastewater with the concentration of organic material unchanged,
(d) fermenting non-degradable organic material in the wastewater from step (c) by using an anaerobic microorganism, whereby the material can be converted into forms that can be easily fed to aerobic microorganisms in subsequent steps; and, also, fermenting the sludge that is returned from step (i) below to produce organic acids,
(e) carrying out Anammox reaction of ammonia in the wastewater with NO2xe2x80x94N in the sludge, which underwent the anaerobic fermentation in step (d) after being returned from step (i),
(f) activating soil microorganisms that are contained as a solid form in a biopond,
(g) feeding the activated microorganisms into a denitrification-inducing aeration tank, which then contributes both to the degradation of organic material and to the nitrification from ammonia nitrogen in the wastewater from step (e) to NO3xe2x80x94N in cooperation with aerobic microorganisms, which already exist in the aeration tank, and mixing to induce denitrification,
(h) denitrificating the wastewater from step (g) by reducing nitrates in the wastewater to nitrogen through endogeneous respiration of the microorganisms under a condition in which oxygen does not exist and external carbon sources are not introduced,
(i) carrying out a solid-liquid separation of the wastewater from the microorganisms and returning a part of the precipitated sludge to step (d) above, and
(j) removing any residue from the supernatant from step (i) by aggregating them and effluenting the finally treated wastewater.
The method of the invention can be carried out by using an apparatus comprising the following elements:
(a) an equalization tank for equalizing the flow rate and concentration of the wastewater that has originated from the source,
(b) a chemical solid-liquid separator for adjusting the concentration of the organic material and nitrogen,
(c) a stripping tank for selectively removing ammonia nitrogen while leaving the concentration of organic material in the wastewater unchanged,
(d) an anaerobic fermenter for both fermenting non-degradable organic material in the wastewater by using an anaerobic microorganism, whereby said organic material can be converted into forms that can be easily fed to aerobic microorganisms in subsequent steps; and for fermenting the sludge that is returned from the sedimentation tank below to produce organic acids;
(e) an Anammox tank for reacting ammonia in the wastewater with NO2xe2x80x94N in said sludge to generate nitrogen gases;
(f) a biopond to contain solidified soil microorganisms and to activate and feed them into a denitrification-inducing aeration tank;
(g) a denitrification-inducing aeration tank for both the degradation of organic material in the wastewater by aerobic microorganisms, which already exist in the aeration tank and are fed from said biopond, and for the nitrification of ammonia nitrogen into NO3xe2x80x94N;
(h) a denitrification tank to reduce nitrates in the wastewater to nitrogen through endogeneous respiration of the microorganisms under a condition in which oxygen does not exist and external carbon sources are not introduced;
(i) a sedimentation tank for solid-liquid separation of microorganisms from the denitrified wastewater in which the organic material has been nearly completely oxidized;
(j) an aggregation-sedimentation tank for aggregating and removing the residual material from the supernatant obtained from said sedimentation tank; and
(k) a dewatering tank for reducing part or all of the water in the sludge discharged from said solid-liquid separator, anaerobic fermenter, sedimentation tank and aggregation-sedimentation tank.
A feature of the invention is the use of solid-liquid separation for reducing in the wastewater the amount of suspended material having a high concentration of organic material, rather than diluting the wastewater.
Another feature of the apparatus is that it includes an ammonia-stripping tank for selective removal of ammonia while not changing the concentration of organic material in the wastewater.
Another feature of the invention is that the apparatus includes a anaerobic fermenter that is designed to allow the sludge sedimented therein to be fermented to produce organic acids. The acids can be utilized in phosphorous removal.
A further feature of the apparatus is that it includes an Anammox tank. In the tank NH4+ and NO2N can be oxidized in the supernatant of the wastewater, which has been returned from a sedimentation tank.
A further feature of the apparatus is that it includes a biopond, which is a structure comprising a biomaker and an air generating unit. The term xe2x80x9cbiomakerxe2x80x9d means a microorganism-activating unit containing a biocomp in a crushed stone bed. The term xe2x80x9cbiocompxe2x80x9d refers to a body having fixed soil microbes. The biopond activates the microorganisms to enhance the efficiency of the wastewater treatment.
The biopond is designed so that the flow of the original wastewater into the biopond can be blocked if desired to starve microorganisms therein. The ability of the microorganism to digest organic material in the wastewater in subsequent steps can be maximized by such blocking.
The aeration tank in the present invention can be divided into four stages, which facilitate the mixing of the microorganisms with the wastewater and the adjusting of the amount of dissolved oxygen. Furthermore, the tank is fitted with a mixer at one end, where air feeding does not occur. Thus, the tank is advantageous in facilitating denitrification and subsequent denitrification.
A further feature of the invention is the use of a sedimentation tank that is designed to feed the sedimented sludge into a biopond and return the supernatant into an Anammox tank. The sludge activates microorganisms in the biopond. The returned supernatant is subjected to nitrogen removal in the Anammox tank.
A further feature of the invention is the use of the aggregation-sedimentation tank, in which residual organic material and nutrients and suspended material can be treated with chemicals and the water quality can be managed stably and efficiently.